MOLECULAR-BEAM SPECTROSCOPY OF MOLECULES WITH LOW VOLATILITY VIA LASER-DESORPTION FROM THIN-FILMS CONTAINING PARTICULATE SILVER

A new polymer matrix containing particulate silver has been developed for the introduction of analytes with low or negligible volatility int o molecular beams via laser desorption. These silver-containing film m atrices (SCFM) permit stable desorption to proceed for extended period s (ca. approximately 10 h) and have been applied successfully to the n ondestructive volatilization of a number of amino acids and a transiti on-metal compound. Analytes can be extracted directly from solution on to the SCFM surface by simply dipping the film into the solution and t hen air-drying the film. The laser desorption apparatus, when coupled to a supersonic molecular beam/laser ionization time-of-flight mass sp ectrometer, permits the detection of the analytes at femtogram levels. Furthermore, we have developed a reel-to-reel tape transport device t hat allows extended usage of the analyte-loaded SFCM, thereby permitti ng the measurement of wavelength-scanned mass-selected resonance-enhan ced multiphoton ionization spectra of analytes with low or negligible volatility. We demonstrate this application with the aromatic amino ac ids L-tryptophan and L-phenylalanine. The degree of cooling achieved i n the molecular expansion is shown to be comparable with that achieved using conventional beam sources, and the desorption yield is sufficie ntly stable for high-quality spectra to be measured.